Method of and apparatus for storing liquefied gas mixtures



Aug. 18, 1942.

METHOD OF AND APPARATUS FOR STORING LIQUEEIED GAS MIXTURES Filed Jan. 14, 1941 INVENTORS HENRY C. KORNEMANN EDWARD F. YENDALL BY ATTORNEY H. c. KORNEMANN ET'AL V I 2 Patented Aug. 18, 1942 METHOD OF AND APPARATUS roa groamc LIQUEFIED GAS MIXTURE Henry C. Kornemann and Edward F. Kenmore, N. Y., assignors to The Products Company,

Yendall, Linde Air a corporation of Ohio Application January 14, 1941, Serial No. 374,332

8 Claims.

This invention relates to a method of and apparatus for storing liquefied gas mixtures at relativelylow temperatures and more particularly to a method of and apparatus for maintaining substantially constant, the proportions of the constituents of a mixture of liquefied gases, when stored at lowtemperatures in insulatedcontainers.

When liquefied gases are stored in insulated containers at relatively low temperatures, below atmospheric temperature, some leakage of heat into the stored liquid inevitably occurs because the commercially available insulating means employed in such containers does not exclude all heat tending to enter the liquid from theenvironment. Thus a small amount of liquid will constantly tend to evaporate and build a pressure "ing point is stored, the evaporation due to heat leak will change the relative composition because the component having the lower boiling point will tend to evaporate preferentially and that the composition of the vapor as well as the composition of the remaining liquid will change, the resulting vapor being initially richer in the component having the lower boiling point and the liquid becoming richer in the component having the higher boiling point.

It is a principal object of the present invention to provide an improved method of and apparatus for storing mixtures of liquefied gases at relatively low temperatures so as to maintain substantially constant the proportions of the constituents in the gas normally evaporated from the stored mixture; for maintaining substantially constant the purity of commercial liquid oxygen when stored at low temperature in-an insulated container; and for insuring that the gas withdrawn from such container shall have a commercially acceptable purity. These and other objects and novel features of this invention will become apparent from the following description and the accompanying drawing which shows a sectional view of an exemplary container for holding a body of liquid oxygen including means for maintaining the purity thereof substantially constantaccording to the ent invention.

The principles of the invention are set iorth in connection with the storage of commercial liquid oxygen as a specific example of a gas mixture since commercial liquid oxygen generally and preferably contains 99.6% pure oxygen; the remainder consisting of substantially liquid argon and nitrogen. Commercial liquid oxygen thus constitutes a gas mixture in which the constituents have substantially diflferent boiling points and when liquid oxygen is stored in the customary insulated container, the slow inflow of heat through the insulation to the liquid causes aslow but constant evaporation of liquid to occur. The vapor that accumulates in the gas space above the liquid in the container is richer in argon and nitrogen and continued evaporation reduces the proportion of argon and nitrogen in the stored liquid. Thus, gas withdrawn from the gas space of such a container.will not comprise 99.6% oxygen but will be of lower purity. It is particularly desirable that all the gas material remaining in and withdrawn from the storage container for commercial use should be of a constant purity. According to the present invention, the heat leak'that normally occurs into a body of stored liquid oxygen is absorbed prior to its entry into the main liquid body, by effecting preferential evaporation of portions of liquid separated from the stored body of liquid and evaporating suificient liquid from such separated portions to remove, by its heat of vaporization, the heat entering the container. The vaporization may be eflfected while the portions being evaporated are in heat exchanging contact with the body of liquid or isolated from such contact.

Referring now to the drawing, a body of liquefied gas, for example, commercial liquid oxygen is indicated at M, stored within a metal vessel H which may be of any suitable shape, for example, cylindrical, spherical, or rectangular as shown. The vessel H is surroundedby a relatively thick .layer of heat insulation l2 which may be of any customary type such as a vacuum insulation or a dry powdered material such as magnesium carbonate. The insulation is held within an outer casing IS. The vessel H is provided with an inner vessel or basket ll of relatively thin metal which is smaller than the vessel II to provide a relatively narrow liquid holding space l5 between it and the wall of the vessel H. The basket l4 may be supported by suitable spacers l6 and is preferably provided with a substantially closed top I] having a relatively small opening l8 principles of the prestherein. The bottom of the basket 14 is provided with an opening l9 to allow liquid to pass from the interior to the space IS. The vessel may be filled by a filling connection 20 that extends through the outer jacket It, the vessel II, and the top I! of the basket. The container is also provided with a bottom liquid withdrawal connection 2| for conducting liquid from the bottom of the basket H and with a gas phase withdrawal connection 22 provided to conduct gas from the top of the vessel H.

The basket l4 may have a single thin sheet metal wall but in most cases it will be preferable to provide the side walls and the bottom of the basket l4 with heat insulation, for example, by

providing the basket 14 with an extra metal wall or jacket 23 spaced from the inner wall 24 to enclose therebetween a layer of suitable heat insulation 25 which may be similar in character to-the insulation l2. When the vessel is filled with a body of liquid 10, theiliquid will flow through the opening l9 and fill the shell-like space l5 between the basket l4 and the vessel II to a level equal to the level of the liquid l0 since the gas pressure outside and inside of the basket I4 is equalized through the opening l8. Heat that enters through the insulation II will be intercepted by the liquid in the space l5 which evaporates at a rate corresponding to the rate of heat leakage. The vapors produced in the shell-like space l5 are prevented from mingling with the vapors above the main body of liquid HI and such vapors pass out through the condit 22. If the top H of the basket were omitted, excessive mixing of the vapor evolved in the space l5 outside of the basket with the vapor immediately above the liquid body I might occur and there would be a tendency to establish equilibrium conditions at the large liquid surface which would result in the vapor having a different compostion than the liquid and tend to defeat the purposes of the invention. As the liquid evaporates from the space IE, it is replenished by liquid flowing through opening l9 from below the mainbody of liquid i0. At first the purity of the liquid in the space IE will increase due to preferential evaporation of nitrogen and argon. This purity will ultimately reach a steady value such that the composition of the vapor evolved in the space I5 is the same as the composition of the main body of liquid. Thereafter as vapor is evolved and the liquid level in space l5 tends to be reduced, additional liquid having the same composition as the vapor and equal in amount to the vapor produced flows into the space l5 through the opening IS. The composition of the liquid in the space outside the basket I4 is thus maintained-at a value corresponding to a greater purity than that of the main body of liquid such that the evaporation therefrom has a composition the same as the main body Ill. The difference in composition between the liquid in the space l5 and the main body l0 will cause the boiling point of the liquid in space l5 to be slightly higher than the boiling point of the body liquid. Therefore there would be a tendency for some heat to flow from the basket M to the main body of liquid l0 and cause some evaporation therefrom which is undesirable. By providing heat insulation 25 for the basket, such undesirable heat transfer is reduced to an immaterial amount and the liquid in space l5 can act to deflect the heat entering the vessel entirely from the main body. of liquid so that its compositionwill not change during a period of storage.

The embodiments described herein and illustrated in the drawing are disclosed to indicate how the invention may be applied. Certain features of, the invention may be used independently of others and changes may be made in the details of the apparatus without departing from the principles of the invention. 7

We claim:

l. A method of maintaining substantially constant the composition of gas evaporated from a liquefied gas mixture when stored in a body at a relatively low temperature in a commercially insulated container which comprises, substantially surrounding said body of liquefied gas with a relatively thin layer of said liquefied gas; supplying portions of liquid to said layer from said body below the surface thereof; and intercepting and absorbing the heat tending to flow toward said body by the evaporation of portions of liquid from said layer,

2. A method according to claim. 1 in which the vapors produced by said vaporization are withdrawn substantially separate from the vapors normally above the liquid surface of said body of liquid.

3. A method according to claim 1 which includes substantially preventing any flow of heat from said layer to said body of liquid.

4. A method of maintaining substantially constant the composition of a liquefied gas mixture when stored in a body at a relatively low temperature in a commercially insulated container which comprises, withdrawing portions of said body of liquid to form an auxiliary body of liquid positioned to intercept heat tending to flow through said insulation toward said stored body of liquid; permitting vaporization of liquid to occur from said auxiliary body of liquid untilathe composition of said auxiliary body becomes such that the vapors produced therefrom become substantially the same in composition as the composition of said stored body of liquid; withdrawing the vapors produced; and then replacing the liquid of said auxiliary body vaporized by said intercepted heat with portions of liquid substantially of equal composition as and equivalent in amount to the vapor being produced.

5. A method according to claim 4 which includes maintaining liquid and gas phase communication between said stored body of liquid and said auxiliary body of liquid and substantially preventing free admixture of said vapors produced with vapor normally above the liquid surfaceof said stored body of liquid.

6. Apparatus for storing a mixture of liquefied gases at low temperature which comprises a container for holding a body of such liquefied gases; heat insulating means surrounding said container; means in said container for maintaining a relatively thin layer of said liquid adjacent the inner walls of said container substantially out of direct contact with said main body of liquid, said layer being in restricted liquid and gaseous communication with said main body of liquid whereby heat inflow through said insulation is counteracted substantially solely by vaporization of liquid from said layer of liquid.

7. Apparatus for storing a mixture of liquefied gases at low temperature which comprises a container for holding a body of such liquefiedgases; heat insulating means surrounding said container; a relatively thin-walled lining within said container, said lining enclosing a main portion of said liquid and providing a relatively thin layer of said liquid adjacent the inner walls of said container, said lining substantially completely enclosing said main portion of liquid and having restricted openings therein disposed above and below the normal surface of said liquid; and a discharge conduit for conducting gas from the upper portion 01' said container and from the space outside of said lining.

8. Apparatus according to claim 7 in which a layer of heat insulation is interposed between said main portion of liquid and said thin layer of liquid. V

5 HENRY C. KORNEMANN.

EDWARD F. YENDALL. 

